The present invention relates to a thermal transfer recording apparatus.
With recent developments in electronic techniques, office automation (OA) is prevalent and a recording apparatus or printer is frequently installed in an office amongst other types of equipment. Of various types of recording apparatus, a thermal transfer apparatus is simple in construction, does not easily allow alteration of recorded information, and allows safe storage of such information. Two types of thermal transfer printers are known. The first type is a serial printer in which a recording head scans transversely together with an ink ribbon for recording along each line. The second type is a line printer in which a thermal head for recording has heating resistors along the entire width for recording. In each type of thermal transfer printer, an ink film as an ink medium is superposed on a recording paper sheet, and a thermal head is urged against the sheet through the ink film, so that the ink is selectively transferred onto the sheet and recording is thus completed.
In a thermal transfer recording apparatus, it is important to ensure tight contact between a thermal head, an ink film and a recording paper sheet, in order to reduce heat resistance and to facilitate ink transfer from the ink film onto the recording paper sheet. In order to ensure tight contact, the ink film is becoming thinner and more flexible.
However, such a thin ink film tends to have an increased number of wrinkles. When there are wrinkles in the ink film, the ink film and the recording paper sheet do not tightly contact each other in places, and desired ink transfer may not be performed thereat. This causes local transfer failure which is one important factor in degrading printing quality. In a serial printer, the width of the ink film is as narrow as several millimeters; it tends not to form wrinkles, and any wrinkles once formed are transferred to the two side portions of the ink film. In a line printer, an ink film of 20 cm width is used wherein an ink is coated to a thickness of several microns on an extremely thin base film of about 10 .mu.m thickness. For this reason, wrinkles tend to form due to expansion/shrinkage of the film base by heat or imbalance in tension between a film portion from which the ink has been transferred and a film portion on which the ink is still coated. The wrinkles thus formed are not easily transferred to the sides of the ink film. Once formed, a wrinkle becomes bigger as printing is performed, and finally causes local transfer failure.
In this manner, a printer utilizing thermal transfer of ink has a problem of local transfer failure due to wrinkles formed in the ink film. This problem is also encountered in a serial printer if the ink film is made thinner or wider in order to improve printing speed or resolution.